The subject of this invention is temporary supports or carrier layers for transfer layers.
Transfer layer sheets and processes are well known and have multiple applications in the electronics industry, for example, for making photoresist masks and solder resist masks and similarly, in the printing industry for making color reproductions and for proofing color separations.
These transfer layer sheets comprise a temporary support, the transfer layer that is carried thereon and, optionally, an intermediate layer.
Synthetic resin films of polyesters, polyamides, polyethylene, polypropylene, polyvinyl chloride and similar materials are used as temporary supports.
The appropriate transfer layer can be light sensitive as well as light insensitive.
Light sensitive transfer layers contain, as significant components, a binder, a light sensitive compound, the solubility of which changes after exposure to light, and a photoinitiator or photoinitiator system. For making color reproductions, the layers can also be colored with an appropriate dyestuff.
Furthermore, light insensitive transfer layers are also known for use in recording on light sensitive layers which contain imagewise tacky and nontacky areas. These transfer layers contain at least one binder and a finely divided powder suitable for production of the image.
In the transfer process, either the entire transfer layer or imagewise areas are transferred from the temporary support onto the permanent support using pressure and/or heat. After the transfer, the temporary support is stripped from the transfer layer. Achieving good results requires that the transfer layer have greater adhesion to the permanent support than to the temporary support.
A common problem of such transfer processes is that the smallest irregularity on the permanent support or the smallest dust or dirt particle on the permanent support, on the transfer layer or on both layers prevents adequate adhesion of the transfer layer to the permanent support, which adversely affects operation of the resist or image reproduction and color reproduction in these areas.
With resist layers, these adverse effects occur primarily during washoff when exposed areas which do not adhere properly to the support are removed, so that the etching solution or the solder material can act on areas that should actually be protected by the resist layer.
In the preparation of color reproductions, inadequate adhesion causes "noncolored" flaws, which are visible as white spots if paper is used as the image receptor. These defects are especially noticeable in continuous tone areas and large area scanning patterns.